Synchrotron radiation photoelectron spectroscopy study on oxides formed at Ge(100)2 × 1 surface in atmosphere

Abstract

Synchrotron radiation photoelectron spectroscopy was applied to conduct chemical analysis of Ge oxides formed at the Ge(100)2 × 1 surface in atmosphere at room temperature. High energy-resolution Ge 3d core-level spectra showed that the ambient-exposed Ge(100) surface has oxidation states with 4+ charge state at maximum, which is in strong contrast to in situ studies on pressure-controlled Ge oxidation in vacuum using pure O2 gas. Adsorbed oxygen amount is considerably lower than that observed for the O2-pressure controlled oxidation of Si(111)7 × 7 surface at saturation. The oxidation of Ge(100) surface proceeds slowly even in atmosphere, indicating that reactivity of Ge surface seems to be low against oxidation in the air. The O 1s spectra after keeping in the air exhibit the (−OH) (hydroxyl group) component, deducing that the water molecule from the ambient humidity likely promotes the oxidation, where oxides may have different chemical configurations from that formed by using O2 gas in vacuum. Our findings will contribute to the basic understanding of oxidation mechanisms and stability of oxides at Ge(100)2 × 1 surface in the air.